<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN""http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <script src="http://apps.bdimg.com/libs/jquery/2.1.1/jquery.min.js"></script>
</head>
<body>
  <input type="file" name="file" id="fileuploade" size="40" />
  <button id="text">大小</button>
</body>
<script type="text/javascript">
  $(function(){
    $("#text").click(function(){
        var obj_file = document.getElementById("fileuploade").files;
        console.log(obj_file);
        alert(obj_file[0].size / 1024);    //精确值  
        alert(Math.ceil(obj_file[0].size / 1024)); // 粗略 KB.
    })
  })
</script>
</html>